Pipes intended for use in deepwater oil fields include risers (pipes through which crude oil is transported upwards), umbilicals (pipes for controlling oil production, which include an assembled unit consisting of a power cable, a pipe carrying a liquid agent for decreasing the viscosity of crude oil, and the like), and flowlines (pipes for transporting produced crude oil on sea beds). These pipes have various structures. Some of them are pipes made of only metal, and some of them are metal/resin hybrid pipes. Currently, there is a trend away from pipes made of only metal and toward metal/resin hybrid pipes, with the aim of reducing the weight. In order to withstand the temperature of produced crude oil which increases with the depth of offshore drilling, resins used for such pipes are required to have good mechanical strength and chemical resistance at high temperature (tolerance to high temperature crude oil, tolerance to acidic gas (e.g. hydrogen sulfide) in crude oil at high temperature, and tolerance to liquid agents (e.g. methanol, hydrogen chloride) to be injected to decrease the viscosity of crude oil at high temperature), and to have low permeability at high temperature. As a result, there is a need for an alternative material usable instead of polyamide (operating temperature limit: 90° C.) and polyvinylidene fluoride (operating temperature limit: 130° C.), which are currently used for these pipes.
Based on the common knowledge that fluororesins such as polyvinylidene fluoride are excellent in performances including chemical resistance, fluororesins such as those noted below have been developed.
Patent Documents 1 to 5 disclose copolymers containing specific amounts of tetrafluoroethylene, vinylidene fluoride, and chlorotrifluoroethylene.
Patent Document 6 discloses a copolymer containing specific amounts of tetrafluoroethylene, vinylidene fluoride and one of chlorotrifluoroethylene and hexafluoropropylene.
Patent Document 7 discloses a copolymer containing specific amounts of tetrafluoroethylene, vinylidene fluoride, and ethylene trifluoride.
Patent Documents 8 to 10 disclose copolymers containing specific amounts of tetrafluoroethylene, vinylidene fluoride, and perfluorovinyl ether.
Patent Document 1: U.S. Pat. No. 3,331,811
Patent Document 2: JP 51-71287 A
Patent Document 3: JP 2-123152 A
Patent Document 4: JP 4-189879 A
Patent Document 5: WO 2007/078916
Patent Document 6: JP 5-295038 A
Patent Document 7: JP 57-123603 A
Patent Document 8: JP 2004-217728 A
Patent Document 9: JP 3-66714 A
Patent Document 10: JP 2004-219579 A